1. Field of the Invention
The present invention relates to a liquid ejection head and an image forming apparatus comprising a liquid ejection head, and more particularly to a liquid ejection head and an image forming apparatus comprising a liquid ejection head that an ejection pressure generating unit for ejecting a liquid and a liquid supply unit are formed in a laminated thin plate structure, in order to increase the density of ejection ports which eject the liquid while improving the liquid supply performance.
2. Description of the Related Art
Conventionally, as an image forming apparatus, an inkjet printer (inkjet recording apparatus) is known which comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (ejection ports) and which records images on a recording medium by ejecting ink from the nozzles toward the recording medium while causing the inkjet head and the recording medium to move relatively to each other.
In this type of inkjet printer, ink is supplied from an ink tank to a pressure chamber through an ink supply passage. A piezoelectric element is then driven by applying to the piezoelectric element an electric signal corresponding to image data, whereby a diaphragm constituting a part of the pressure chamber is deformed such that the volume of the pressure chamber decreases. As a result, the ink in the pressure chamber is ejected from the nozzle in liquid droplet form.
In the inkjet printer of this kind, the ink is supplied to pressure chambers from an ink tank via an ink supply channel, and piezoelectric elements are driven by supplying electrical signals corresponding to the image data to the piezoelectric elements. Thereby, the diaphragm constituting a portion of each pressure chamber is deformed, the volume of the pressure chamber is deformed, and the ink inside the pressure chamber is ejected from a nozzle in the form of a droplet.
In the inkjet recording printer, one image can be formed on a recording by combining dots formed by ink ejected from the nozzles. In recent years, it has become desirable to form images of high-quality on a par with photographic prints, according to inkjet printers. It has been considered that high image quality can be achieved by reducing the size of the ink droplets ejected from the nozzles by reducing the diameter of the nozzles, while also increasing the number of pixels per image by arranging the nozzles at high density.
Conventionally, various proposals have been made for increasing the density of the nozzle arrangement, and improving the ink supply efficiency so that a higher print speed can be achieved.
For example, it is known that an ink supply channel supplying the ink to a pressure chamber is provided in a diaphragm forming one surface of the pressure chamber while a reservoir (common liquid chamber) is formed on the rear surface of the diaphragm so that ink is supplied from the reservoir to the pressure chamber through the ink supply channel, thereby achieving a high-density nozzle arrangement (see Japanese Patent Application Publication No. 9-226114, for example).
For example, it is also known that a piezoelectric element is provided on the opposite surface of the pressure chamber to the surface in which the nozzle is formed, an ink supply reservoir is disposed on the piezoelectric element side, a cover is provided over the piezoelectric element, and an electrode is extracted by wire bonding or a thin plate, thereby simplifying the structure of the apparatus (see Japanese Patent Application Publication No. 2000-127379, for example).
For example, it is also known that a piezoelectric actuator is disposed on a nozzle face side of a pressure chamber while the inkjet head is formed by Si photoetching so that an aluminum plug passes through laminated layers, thereby achieving a high density and a low cost (see Japanese Patent Application Publication No. 2000-289201, for example).
For example, it is known that a supply restrictor is provided in a diaphragm, an ink supply tank serving as an ink supply unit is provided on the opposite side of a piezoelectric element to a pressure chamber, and an ink supply port connected with the pressure chamber is formed so as to pass through the diaphragm from the ink supply tank. In this case, the ink supply unit functions as an insulating seal for the piezoelectric element, and also functions as a cover for the piezoelectric element and a damper. Therefore, an increase in the number of nozzles, a reduction in cost, and an increase in precision can be achieved (see Japanese Patent Application Publication No. 2001-179973, for example).
For example, it is known that a porous member having a large number of small internally-connected holes, such as a sintered stainless steel, is used as an ink supply layer so as to be able to pass through the ink, in order to realize an inkjet head which has an improvement of refilling, a high print speed, a high confidence, an ability to mix many types of ink, and an excellent filtration property (see Japanese Patent Application Publication No. 2003-512211, for example).
Since a common ink chamber (common liquid chamber) between the piezoelectric element and a power board formed with wiring which supplies drive signals for driving the piezoelectric element are provided in order to shorten the supply and ejection flow channel from the pressure chamber to the nozzle, then it is effective for achieving high-speed printing with a high-viscosity liquid and high-density wire packaging. However, in the case in which the common liquid chamber is disposed on the piezoelectric element side of the pressure chamber as described in Japanese Patent Application Publication Nos. 9-226114 and 2000-127379, for example, if the common liquid chamber is provided on the exterior of the power surface of the piezoelectric element, then the supply flow channel for supplying ink to the pressure chamber increases in length. In particular, when high-viscosity ink is used, the refillability of ink tends to deteriorate. In addition, since the ink supply channel passes through the power surface, then the packaging density is likely to decrease.
Furthermore, when the common liquid chamber is provided on the nozzle side of the pressure chamber as described in Japanese Patent Application Publication No. 2000-289201, for example, the length of the ejection flow channel from the pressure chamber to the nozzle is increased. In particular, when a highly viscous liquid is used, it causes a decrease in responsiveness.
Moreover, the conventional method of forming the pressure chamber and reservoir (common liquid chamber) from silicon causes the cost to increase, and it is difficult to increase length. Additionally, the resin molding has a problem that the finished form, finishing precision, rigidity, and coefficient of linear expansion are insufficient. For example, in Japanese Patent Application Publication No. 9-226114, a silicon photoetching process leads to the increase of cost and the difficulty in elongation of the head. In addition, there is no detailed description of the reservoir or signal circuit connections in Japanese Patent Application Publication No. 9-226114.
In Japanese Patent Application Publication No. 2000-127379, since the reservoir is disposed on a side face, then it is unsuitable for a matrix-form (two-dimensional) nozzle array.
In Japanese Patent Application Publication No. 2001-179973, there is no specific illustration of the construction method for the ink supply unit, and it is difficult to adopt a matrix structure in the illustrated form.
In Japanese Patent Application Publication No. 2003-512211, a bump is formed on both sides of an insulating plate, and then an electrode is taken out by pressurizing the piezoelectric element using an elastic pad. However, it is difficult to achieve increased density, and the connection tends to be unstable.